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    SubjectRe: [PATCH RESEND v4 7/9] KVM: VMX: Handle SPP induced vmexit and page fault
    On Tue, Aug 20, 2019 at 09:44:35PM +0800, Yang Weijiang wrote:
    > On Mon, Aug 19, 2019 at 05:04:23PM +0200, Paolo Bonzini wrote:
    > > On 19/08/19 16:43, Paolo Bonzini wrote:
    > > >> + /*
    > > >> + * Record write protect fault caused by
    > > >> + * Sub-page Protection, let VMI decide
    > > >> + * the next step.
    > > >> + */
    > > >> + if (spte & PT_SPP_MASK) {
    > > > Should this be "if (spte & PT_WRITABLE_MASK)" instead? That is, if the
    > > > page is already writable, the fault must be an SPP fault.
    > >
    > > Hmm, no I forgot how SPP works; still, this is *not* correct. For
    > > example, if SPP marks part of a page as read-write, but KVM wants to
    > > write-protect the whole page for access or dirty tracking, that should
    > > not cause an SPP exit.
    > >
    > > So I think that when KVM wants to write-protect the whole page
    > > (wrprot_ad_disabled_spte) it must also clear PT_SPP_MASK; for example it
    > > could save it in bit 53 (PT64_SECOND_AVAIL_BITS_SHIFT + 1). If the
    > > saved bit is set, fast_page_fault must then set PT_SPP_MASK instead of
    > > PT_WRITABLE_MASK.
    > Sure, will change the processing flow.
    >
    > > On re-entry this will cause an SPP vmexit;
    > > fast_page_fault should never trigger an SPP userspace exit on its own,
    > > all the SPP handling should go through handle_spp.
    Hi, Paolo,
    According to the latest SDM(28.2.4), handle_spp only handles SPPT miss and SPPT
    misconfig(exit_reason==66), subpage write access violation causes EPT violation,
    so have to deal with the two cases into handlers.
    > > Paolo

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